A gyratory crusher of the kind stated above can be used for crushing, for example, ore and stone material into a smaller size. A gyratory crusher is usually provided with a crusher shaft and a crushing head, which is mounted about the shaft and arranged to support a first crushing shell in the form of an inner shell. The gyratory crusher further has a frame on which a second crushing shell in the form of an outer shell is mounted. The second crushing shell defines, together with the first crushing shell, a crushing gap into which the material to be crushed can be introduced.
In the course of the crushing operation, the crushing shells are worn down, which means that they need to be replaced at regular intervals. Replacing the first crushing shell, which is mounted on the crushing head, usually implies loosening a fixing nut or screw. In US 2006/0113414, it is described how loosening a fixing screw has included, historically, relatively laborious measures, such as the use of a blowtorch and sledgehammer. In view thereof, US 2006/0113414 discloses an alternative solution including a blocking plate, which is arranged to press the first crushing shell towards the crushing head. The blocking plate is secured by means of bolts to a threaded stud, which is in threaded engagement with the crusher shaft. The blocking plate is provided with notches that engage corresponding lugs or ears on the first crushing shell. Due to the crushing process, the first crushing shell will be rotated about the crushing head. As a consequence, the first crushing shell will cause also the blocking plate to rotate, which in turn will rotate the threaded stud with the result that it is screwed down into the crusher shaft, thereby ensuring that the first shell is secured to the crushing head.
A drawback of the securing device disclosed in US 2006/0113414 is that it requires mounting of a great number of parts for securing the first crushing shell to the crushing head, and that the bolts used to secure the blocking plate on the threaded stud are subjected to high loads.